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Hi, I know nothing about bikes but recently inherited a harlem toscano mountain bike.

I took it into halfords for a brake & gears service to ensure it was safe to use. They replaced some cables and the break pads, so all good.

I noticed that everytime I went up hill when changing gears the chain would come off. So I took it back and complained and they checked it again and replaced the chain and the back gear cogs. However they said the problem was because its a 6 speed shifter for 7 speed cog. I dont really understand what that means.

There is six cogs on the back and six numbers on the gear shifter on the right handlebar. there are three cogs on the front part of the gears and they are controlled by the other shifter and the chain seems to come off when its trying to get on to the smallest cog on the front.

Can anyone explain to me whats happening as Im confused.
Well, one thing that's going on is you need a better mechanic. Either you completely misunderstood what they're telling you (in which case, they should explain it better), or they've managed to have you bring in the bike twice, and charge you, and still haven't fixed it.

Maybe there's something incompatible about the shifter and gear cluster. You could post some pics of the two and we might see something. But there's a few other things that could cause what you're experiencing.

I think what you're describing is that the chain comes completely off of the gears and you have to grab the chain and put it back on. Is that right? Is it falling off in the front or the rear?

If in front, then most likely either the front derailleur is mis-aligned and/or the "limit screws" aren't set right. These would be basic adjustments for any mechanic checking your gears.

If it's falling off in the back, again could be limit screws or possible a bent derailleur hanger which can make it very hard to get the gears adjusted right.

I would try to call up the shop again and see if they can give you a better description of what they're saying is wrong. Maybe you misunderstood.

I will also point out that if this only happens when you're shifting going uphill, you're probably putting a lot of force on the pedals when you shift at those times. Most bikes need you to really let off the pressure while the shift is occurring so you have to think ahead a bit and plan your shift before the last second. This is common among riders and it just takes a little practice to get the trick of momentarily letting the pressure off until he shift is completed.

Give us some pics if you can and a little more detail on what they told you and what actually happens. We should be able to find the issue.
(06-24-2014, 06:52 PM)griffsr Wrote:  ....everytime I went up hill when changing gears the chain would come off. ....... the chain seems to come off when its trying to get on to the smallest cog on the front.

This can be quite difficult to adjust - and on some bikes impossible. The problem is, when the FD is adjusted so that it is quiet and will always move the chain to the smallest front ring when on the largest back ring; it will push the chain past the smallest front ring when the chain is on a middle cog at the back.

There are chain keepers - several different brands, for example: http://www.amazon.com/dp/B001CJXEKG/
which prevent the chain from over running the smallest chain ring.

One thing that usually works is to shift to the smallest ring in the front only when you are on the largest cog at the back.

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